What is creatine kinase?

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Creatine kinase (CK), also known as creatine phosphokinase (CPK), is a tissue enzyme that converts creatine into phosphocreatine (PCr). Creatine kinase needs to consume one adenosine triphosphate molecule (ATP) and convert it to an adenosine diphosphate molecule (ADP) in order for conversion to occur.

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This biochemical reaction is important for tissues that use ATP quickly. ATP is the energy source for the body; muscle and brain tissues that require large amounts of energy consume ATP rapidly. Creatine kinase uses an ATP molecule to convert creatine into phosphocreatine. This process can be reversed, making creatine kinase an important enzyme to maintain the balance of ATP in many tissues. An example is the phosphocreatine present in the tissue cells can be used by creatine kinase to create ATP for high-energy muscle and brain tissue for use.

Phosphocreatine is often present in abundance in muscle and brain tissue cells as an energy reservoir when ATP levels diminish. Once there is a critical minimum of usable ATP in the cell, a biochemical signal slightly changes the shape of creatine kinase. This therefore changes the function. Creatine kinase then uses an ADP molecule and phosphocreatine present in the cell to create creatine and a usable ATP molecule.